Cut-off systems typically comprise a clamping and shearing assembly called a cut-off die set. Cut-off die sets are well known, see for example U.S. Pat. Nos. 4,108,029; 4,109,555; 4,294,147 and 4,766,792. The die set often comprises upper and lower platens interconnected by a combination of guide bushings and pins enabling he platens to act with reciprocal motion. Typically, a vertical shearing blade is mounted to the upper platen and during the cutting stroke the motion of the upper platen actuates clamping jaws causing the die set to be clamped to the moving stock. Continued motion of the upper platen causes the shearing blade to sever a length of the stock emanating from the mill. The cut-off die set is supported during the cutting stroke by a carriage assembly slidably mounted on a set of rails secured to the press bed. This arrangement allows the die set to travel with the stock during the cut and obviates the need to stop the stock each time a cut is made.
The cut-off die must be specifically aligned and secured to the carriage for proper operation during the cutting stroke. Larger tubing sizes require a corresponding increase in the size of the die set. Increasing the size of the die set requires additional time and effort to align and secure the die set to the carriage.
It is important to note that time is of the essence in the tube cutting industry. Tubing continuously emanates from a tubing mill at a high rate of speed, any stoppage of the mill for repairs or replacement of parts results in lost production and revenue for the tube maker. Therefore, any time savings resulting from ease in maintenance or replacement of the die set increases the efficiency of the mill. As in all machine industries, less down time means greater production. The quicker a die set may be removed and replaced the less the mill is down and converselY the greater the production output.
While other mechanical systems have been developed for locating and securing a die set, such as clamps or spring loaded wedges, these devices are not easily adaptable to the moving carriage of a cut-off press. These devices fail to maintain the positive locking force required to keep the die set securely positioned during the rapid motion and change in forces occurring during the cutting stroke.